Hydrophobic dispersants used in forming polymer dispersions

Abstract: A process for the preparing a water soluble polymer dispersion which comprises polymerizing a water soluble mixture which comprises: (a) a cationic monomer represented by the general formula (I) as defined herein, and/or a second cationic monomer represented by the general formula (II) as defined herein; and (b) (meth)acrylamide in an aqueous solution of a polyvalent anion salt; wherein the polymerization is carried out in the presence of a hydrophobic dispersant which comprises a copolymer of diallyldimethylammonium chloride and a hydrophobic monomer and a hydrophobic dispersant used in forming polymer dispersions which comprises a copolymer of diallyldimethylammonium chloride and a hydrophobic monomer selected from the group consisting of: dialkylaminoalkylacrylates having C₆ to C₂₀ quaternaries, dialkylaminoalkylmethacrylates having C₆ to C₂₀ quaternaries, dialkylaminoalkylacrylamides having C₆ to C₂₀ quaternaries, dialkylaminoalkylmethacrylamides having C₆ to C₂₀ quaternaries, and alkyl esters of acrylic acid.

Description: The present invention relates to a process for preparing a dispersion of a water-soluble polymer which is widely used as, e.g. flocculating agents for waste water treatment, dehydrating agents, chemicals used in papermaking processes, dispersion dispersants for various suspensions, soil improvers, etc. and for preparing dispersions of cationic vinyl addition polymers in an aqueous salt solution. BACKGROUND OF THE INVENTION Conventional processes for the preparation of a water soluble cationic polymer which is useful as a flocculant for waste water disposal or as a papermaking chemical include standing polymerization in an aqueous solution, water-in-oil emulsion polymerization, and suspension polymerization in a hydrophobic solvent. Others have prepared a water soluble, nonionic or anionic polymer by precipitation polymerization in an aqueous solution of ammonium sulfate. Still others have carried out the polymerization in an aqueous solution of salt in the presence of a polyhydric alcohol or a polyelectrolyte as a dispersant. US-A-4 929 655 discloses a process for preparing a water soluble polymer dispersion which overcomes the many disadvantages of the stationary polymerization, water-in-oil type emulsion polymerization and suspension polymerization processes. This process for the production of a water soluble polymer dispersion includes the polymerization of water soluble monomers of 5 to 100 mole % of a cationic monomer represented by the following formula (I), 0 to 50 mole % of another cationic monomer represented by the following formula (II) and 0 to 95 mole % of (meth)acrylamide in the presence of 1 to 10% by weight of an organic high molecular multivalent cation comprising a water soluble polymer containing at least a monomer of formula (II) (i.e., a hydrophilic monomer), based on the total weight of the monomers, in an aqueous multivalent anionic salt solution having a concentration of 15% by weight or more: where R 1 is either hydrogen or CH 3 ; R 2 and R 3 are each an alkyl group having 1 to 3 carbon atoms; A 1 is either an oxygen atom or NH; B 1 is either an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group, and X 1 ⊖ is an anionic counterion, and optionally a second cationic monomer represented by the following general formula (II): where R 4 is either hydrogen or CH 3 ; R 5 and R 6 are each an alkyl group having 1 to 2 carbon atoms; R 7 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms; A 2 is either an oxygen atom or NH; B 2 is either an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group and X 2 ⊖ is an anionic counterion. US-A-5 006 590 provides for a dual dispersant system wherein polymerization is carried out in the presence of: (1) a water soluble cationic polymer which is insoluble in an aqueous solution of a polyvalent anion salt; and (2) a water soluble cationic polymer which is soluble in an aqueous solution of a polyvalent anion salt. The water soluble cationic polymer that is insoluble in the aqueous solution of polyvalent anion salt contains at least 5 mole % of cationic monomer units represented by the aforementioned general formula (I) above and the water soluble cationic polymer that is soluble in the aqueous solution of a polyvalent anion salt contains at least 20 mole % of cationic monomer units represent by the general formula (II) above. Although the final polymer dispersion viscosities were satisfactory, i.e. 1,000 mPa.s (cps) or below, the processes disclosed in US-A-4 929 655 and 5 006 590 proceed through very high process viscosities (i.e., >100,000 mPa.S (cps), which require the use of a custom built high viscosity polymerization reactor. Due to these high process viscosities, the methods disclosed in US-A-4,929,655 and 5,006,590 can only be used in the synthesis of polymer systems containing low polymer contents (i.e., 15 to 20%). That is, in the precipitation processes discussed above, the polymer (acrylamide (AcAm)/dimethylaminoethylacrylate benzyl chloride quaternary (DMAEA.BCQ)/dimethylaminoethylacrylate methyl chloride quaternary (DMAEA.MCQ)) particle is adsorbed or grafted by dispersants such as poly(DMAEA.MCQ) and colloidal stabilization is attained. During this process the hydrodynamic volume of the particle, consisting of water, salt, monomers, macro radical, and dispersant, is significantly increased. This increase is presumably due to the hydrophilic nature of Poly(DMAEA.MCQ) which is highly extended in the polymerization medium. The increase in hydrodynamic volume results in a relative increase in the bulk viscosity. DE-A-2 951 798 refers to water-insoluble graft copolymer particles used as fillers for papermaking. Such water-insoluble graft copolymer particles are prepared by graft copolymerization of at least one specific ethylenically unsaturated monomer and a water soluble cationic prepolymer in the presence of a free radical initiator. The object underlying the invention described therein is to provide organic pigments which can be used as fillers for light paper in order to make it non-opaque, glossy and smooth without deteriorating its strength. The present inventors believe that if the dispersant has a certain degree of hydrophobicity, the polymer particle's hydrodynamic volume will be constrained. That is, if the continuous phase is water and the hydrophobic moieties prefer to be away from water and tend to associate, then a contraction in the particle hydrodynamic volume will occur. This reduction will, in turn, reduce the bulk viscosity. The present inventors have discovered through extensive experimentation, that hydrophobically modified diallyldimethylammonium chloride (DADMAC) polymers can be used as colloidal dispersants in the polymer dispersion precipitation process. This hydrophobic system is at least partially soluble in water as well as in aqueous salt solutions. The hydrophobicity associated with these polymers has been demonstrated to facilitate the precipitation process, presumably reduce the hydrodynamic volume of the resulting particle and thereby very significantly reduce the process viscosity. This allows the production of high molecular weight polymer dispersions in a conventional latex-type reactor, thereby avoiding the substantial costs associated with high viscosity custom built polymerization reactors. Further, the reduction in process viscosity will allow the preparation of polymer systems containing higher actives in reactors that could accommodate high process viscosities. The present inventors have also determined the effect of salt concentration, stabilizer concentration, initiator concentration, shear, temperature and co-stabilizer concentration on the process viscosity. They have also developed optimum process conditions and demonstrated in Figs. 1-4, attached hereto, the extreme sensitivity of these parameters on the process viscosity. That is, in dispersion processes, monomers are soluble in the polymerization medium and present in a homogenous state. The resulting polymer of this process is insoluble in the polymerization medium and introduces the heterogeneous state. As a result of this feature, dispersion processes proceed through a nucleation stage wherein colloidal particles are formed. These colloidal particles grow and reach a critical radius and then phase separate. These particles are typically stabilized by steric stabilizers. The nature of a stabilizer determines its extension into the polymerization medium. Dispersion viscosity (η) is generally explained as a function of the volume fraction (Φ) and the viscosity of the medium, η o . The volume fraction of a particle is governed by the nature of the stabilizer and is derived by the following equation: Φ 1 = Φ(1 + d/a) 3 where a is the radius of the particle, d is the molecular extension of the particle/stabilizer system, Φ is the core-particle volume fraction and Φ 1 is the effective volume fraction. In Einstein, A. Investigations on the Theory of the Brownian Motion, Dover , New York, 1956, an equation was put forth which related the volume fraction of a particle to the dispersion viscosity, i.e., η = η o (1 + [η]Φ + k 2 Φ + 0[Φ 3 ]) where η is the viscosity of the dispersion, η o is the viscosity of the polymerization medium, [η] is intrinsic viscosity (determined by Einstein, to be 2.5 for uncharged particles) and k 2 is a coefficient for interaction between two colliding particles (i.e., 6.2). The Einstein equation can also be written as follows: η = η o (1 + [η]Φ) and a small increase in viscosity due to a small increment in volume fraction can be expressed as, dη = η o [η]dΦ and for an infinitesimal increment to the viscosity η, d η = η[η]dΦ The contribution of particles to the free volume is given by, dΦ (1 - Φ / Φ m ) where Φ m is the maximum packing fraction. The following equation found in Krieger, I.M. Adv. Coll and Interface Sci., 1972, 3, 111, provides the final effect and is given below: η = η o [1 - Φ / Φ m ] - [η]Φ m Thus, any difference in the extension of the stabilizer into the polymerization medium will significantly influence the dispersion viscosity. The stabilizer disclosed in US-A-5,006,590 and 4,929,655 uses a hydrophilic stabilizer viz., polymers based on acrylamide and dimethylaminoethylacrylate methyl chloride quaternary. Due to their hydrophilic nature these systems extend farther into the dispersion medium. The hydrophobic stabilizer of the present invention reduces such an extension due to the associating properties of hydrophobic moieties. This reduction, as shown in the above equations, subsequently reduces the process viscosity. This reduced particle size is related to the reduction in hydrodynamic volume by the Stokes-Einstein equation: D = kT / 6πrη The present invention also provides many additional advantages which shall become apparent as described below. SUMMARY OF THE INVENTION The object of the present invention is to provide a process for preparing a water-soluble dispersion which allows the preparation of polymer systems containing higher actives in reactors that could accommodate high process viscosities. This object can be achieved by using a hydrophobically associating dispersant in forming polymer dispersions which comprises a copolymer of diallyldimethylammonium chloride (DADMAC) and a hydrophobic monomer selected from the group consisting of C 6 -C 20 N-substituted quaternary dialkylaminoalkylacrylates (DMAEA), C 6 -C 20 N-substituted quaternary dialkylaminoalkylmethacrylates (DMAEM), C 6 -C 20 N-substituted quaternary dialkylamino-alkyl(meth)acrylamides, and alkyl esters of acrylic acid. This hydrophobically associating dispersant used according to the present invention is particularly useful in preparing water-soluble polymer dispersions. Subject-matter of the present invention is a process for preparing a water-soluble polymer dispersion which comprises polymerizing a water-soluble mixture comprising (a) a cationic monomer represented by general formula (I): where R 1 is either hydrogen or CH 3 ; R 2 and R 3 are each an alkyl group having 1 to 3 carbon atoms; A 1 is either an oxygen atom or NH; B 1 is either an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group, and X 1 ⊖ is an anionic counterion, and optionally (b) a second cationic monomer represented by general formula (II): where R 4 is either hydrogen or CH 3 ; R 5 and R 6 are each an alkyl group having 1 to 2 carbon atoms; R 7 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms; A 2 is either an oxygen atom or NH; B 2 is either an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group, and X 2 ⊖ is an anionic counterion, and (c) (meth) acrylamide in an aqueous solution of a polyvalent anion salt, the process comprises: conducting said polymerization in the presence of a polymerization initiator and a hydrophobically associating dispersant comprising a copolymer of diallyldimethylammonium chloride (DADMAC) and a hydrophobic monomer selected from the group consisting of C 6 -C 20 N-substituted quaternary dialkylaminoalkylacrylates (DMAEA), C 6 -C 20 N-substituted quaternary dialkylaminoalkylmethacrylates (DMAEM), C 6 -C 20 N-substituted quaternary dialkylaminoalkyl(meth)acrylamides, and alkyl esters of acrylic acid, in a molar ratio of diallyldimethylammonium chloride to hydrophobic monomer in the range between 99:1 and 20:80, wherein said cationic monomer represented by formula (I) (monomer (a)) being present in an amount between 5 and 50 mole%, said cationic monomer represented by formula (II) (monomer (b)) optionally being present in an amount between 5 and 50 mole%, said (meth)acrylamide (monomer (c)) being present in an amount in the range between 20 and 95 mole%, and said hydrophobically associating dispersant being present in an amount between 2.5 and 10 weight%, based on the total weight of monomers (a), (b) and (c). According to preferred embodiments of the process of the present invention the dispersant is a copolymer of diallyldimethylammonium chloride and a monomer selected from the group consisting of dimethylaminoethylacrylate benzyl chloride quaternary and dimethylaminoethylacrylate cetyl chloride quaternary, or a copolymer of diallyldimethylammonium chloride and a monomer selected from the group consisting of dimethylaminoethylmethacrylate benzyl chloride quaternary and dimethylaminoethylmethacrylate cetyl chloride quaternary. The preferred alkyl ester of acrylic acid used according to the present invention is ethylhexyl acrylate. The monomers of formula (I) used in the process of the present invention are preferably selected from the group consisting of the benzylchloride quaternaries of dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide and dimethylhydroxypropyl (meth)acrylate, diethylaminopropyl (meth)acrylamide and dimethylaminohydroxypropyl (meth) acrylate. The monomers of formula (II) used in the process of the present invention are preferably selected from the group consisting of the methyl and ethyl quaternary salts of dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide and dimethylhydroxypropyl (meth)acrylate. The process viscosity during polymerization in the process of the present invention is preferably less than about 5,000 mPa.s (cps). The process of the present invention is particularly suitable for preparing dispersions of cationic vinyl addition polymers in an aqueous salt solution. Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph plotting process viscosity versus salt concentration; Fig. 2 is a graph plotting process viscosity versus co-stabilizer concentration; Fig. 3 is a graph plotting process viscosity versus stabilizer IV; and Fig. 4 is a graph plotting process viscosity versus stabilizer hydrophobicity. DESCRIPTION OF THE PREFERRED EMBODIMENTS The hydrophobically associating dispersant used according to the present invention is used to prepare water-soluble polymer dispersions. These dispersants are copolymers of diallyldimethylammoniumchloride (DADMAC) and a hydrophobic monomer selected from the group consisting of: C 6 -C 20 N-substituted quaternary dialkylaminoalkylacrylates (DMAEA), C 6 -C 20 N-substituted quaternary dialkylaminoalkylmethacrylates (DMAEM), C 6 -C 20 N-substituted quaternary dialkylamino-alkyl(meth)acrylamides, and alkyl esters of acrylic acid. The DADMAC can be prepared in accordance with any conventional manner such as the technique described in US-A 4 151 202. The C 6 -C 20 N-substituted quaternary dialkylaminoalkylacrylate is preferably selected from the group consisting of: dialkylaminoalkylacrylates having C 6 to C 20 chloride quaternary, e.g., dimethylaminoethylacrylate benzyl chloride quaternary or dimethylaminoethylacrylate cetyl chloride quaternary. The C 6 -C 20 N-substituted quaternary dialkylaminoalkylmethacryle is preferably selected from the group consisting of: dialkylaminoalkylmethacrylates having C 6 to C 20 chloride quaternary, e.g., dimethylaminoethylmethacrylate benzyl chloride quaternary or dimethylaminoethylmethacrylate cetyl chloride quaternary. The hydrophobic dispersant used according to the present invention has a molar ratio of diallyldimethylammonium chloride to hydrophobic monomer in the range between 99:1 to and 20:80, preferably 90:10. A semi-batch process is preferably used to make the hydrophobic dispersants and comprises the following steps: a. adding diallyldimethylammonium chloride to a polymerization reaction vessel in an amount between 1 and 19 weight percent; b. heating the diallyldimethylammonium chloride to a temperature in the range between 47°C and 57°C; c. adding a polymer initiator dropwise to the diallyldimethylammonium chloride in an amount between 0.05 and 0.40 weight percent; d. adding a hydrophobic monomer dropwise to the diallyldimethylammonium chloride in an amount between 3 and 19 weight percent; and e. heating the mixture of diallyldimethylammonium chloride, polymer initiator and hydrophobic monomer to a temperature in the range between 47°C and 82°C. Typically, deionized water is added periodically as needed during the polymerization process in a total amount between 63 and 88 weight percent. In some instances it is preferable to mix diallyldimethylammonium chloride with NaCl and deionized water prior to addition to the reaction vessel. The NaCl is added in an amount between 2 and 3.5 weight percent and the deionized water is added in an amount between 1 and 2.5 weight percent. This diallyldimethylammonium chloride solution has a concentration of diallyldimethylammonium chloride in the range between 50 and 65. This semi-batch process produces a hydrophobic dispersant with a pH in the range from 3.5 to 4.5. The diallyldimethylammonium chloride, polymerization initiator and hydrophobic monomer are heated at a temperature in the range between 47°C and 57°C for a period of 6 to 8 hours. Thereafter, the temperature of the reaction vessel is increased to 72°C to 82°C for a period of between 5 and 7 hours. After polymerization has been completed the copolymer product is typically diluted with deionized water, cooled and stored. The polymerization initiator is selected from the group consisting of 2,2'-azobis(2-amidinopropane) hydrochloride (V50), ammonium persulfate, 2,2'-azobis(N,N'-dimethylene isobutyramidine) dihydrochloride (VA044), and ammonium persulfate/sodium meta bisulfite. The dispersant used according to the present invention is particularly useful in processes for preparing a water soluble polymer dispersion by polymerizing a water soluble mixture of a cationic monomer represented by the following general formula (I): where R 1 is either hydrogen or CH 3 ; R 2 and R 3 are each an alkyl group having 1 to 3 carbon atoms; A 1 is either an oxygen atom or NH; B 1 is either an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group, and X 1 ⊖ is an anionic counterion, and optionally a second cationic monomer represented by the following general formula (II): where R 4 is either hydrogen or CH 3 ; R 5 and R 6 are each an alkyl group having 1 to 2 carbon atoms; R 7 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms; A 2 is either an oxygen atom or NH; B 2 is either an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group and X 2 ⊖ is an anionic counterion, and (meth)acrylamide in an aqueous solution of a polyvalent anion salt; wherein the polymerization is carried out in the presence of a dispersant which comprises a copolymer of diallyldimethylammonium chloride and a hydrophobic monomer as listed above and in the presence of a polymerization initiator. The (meth)acrylamide is typically present in an amount in the range between 20 and 95 mole %, the cationic monomer represented by the general formula (I) is typically present in an amount between 5 and 50 mole %; and the cationic monomer represented by the general formula (II) is typically present in an amount between 5 and 50 mole %. The use of the cationic monomer represented by the general formula (II) is optional. The dispersant is present in an amount between 2.5 and 10 weight %, based on the total weight of the monomers of the dispersion. Examples of monomers represented by the general formula (I) include quaternary monomers obtained by treating dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide and dimethylhydroxypropyl (meth)acrylate, diethylaminopropyl (meth)acrylamide and dimethylaminohydroxylpropyl (meth)acrylate with benzyl chloride. One preferred monomer is N-benzyl-N-(meth)acryloyloxyethyl-N,N-dimethylammonium chloride. Examples of monomers represented by the general formula (II) include salts such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide and dimethylhydroxypropyl (meth)acrylate, and methylated and ethylated quaternary salts. One preferred monomer is N-(meth)acryloyloxyethyl-N,N,N-trimethyl ammonium chloride. The multivalent anionic salt used to deposit the polymer in the present invention is a sulfate or a phosphate, and typical examples of these salts include ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammonium hydrogenphosphate, sodium hydrogenphosphate and potassium hydrogenphosphate. The salt is used in the form an aqueous solution at a salt concentration of 15.75% or more, preferably 16.5% by weight or more. The dispersant used in this invention is at least partially soluble in both water and the aqueous salt solution. Utilizing the dispersant permits the use of conventional latex reactors since the process viscosity during polymerization is maintained below about 5,000 mPa·s (cps) more preferably below about 3,000 mPa·s (cps). The present invention can best be understood by reference to the following working and comparative examples. Preparation - EXAMPLE 1 A dispersant was formed from diallyldimethylammonium chloride (DADMAC) and dimethylaminoethylmethacrylate cetyl chloride quaternary (DMAEM.CCQ) monomers using a batch process. The following reagents were used: 251.30 g 62% Solution of DADMAC 150.00 g 20% Solution of DMAEM.CCQ 0.30 g Versene 10.00 g Adipic Acid 15.00 g 25% Solution of Ammonium Persulfate 75.08 g Deionized Water DADMAC was added to a mixture of DMAEM.CCQ, adipic acid, versene, and deionized water. This reaction mixture was then heated to about 50°C and thereafter the ammonium persulfate was added. The reaction vessel was purged with nitrogen at 10 ml/min. and stirred at about 250 rpm. After 30 minutes a precipitate began to form so an additional 154.76 g of a 62% solution of DADMAC, 10 g of a 25% solution of ammonium persulfate and 0.10 g of versene were added to the reaction vessel. Thereafter, the temperature of mixture was increased to 65°C for 6 hours and then cooled to ambient temperature. The final molar ratio of DADMAC to DMAEM.CCQ was 96.68% to 3.32%. A preparation of DMAEM.CBQ (dimethylaminoethylmethacrylate cetyl bromide quaternary) was effected as follows: 80.00 g 97% Cetyl Bromide 40.00 g 99% DMAEM 0.08 g Hydroquinnone 500.00 g Ethanol The above reactants were combined and heated at reflux for 4 hours. The solvent (i.e., ethanol) was removed under reduced pressure. A gummy liquid upon cooling afforded pale pink colored solid DMAEM.CBQ monomer in 96% yield. This monomer was then dissolved in deionized water to a desired dilution. The preparation of DMAEM.CCQ was effected by stirring an aqueous solution (25% actives) of DMAEM.CBQ (1,000 g), prepared as above, with Amberlite IRA-400 (Cl - ) ion exchange resin for 30 minutes. The resin was filtered and the monomer used in subsequent polymerizations. Preparation - EXAMPLE 2 A dispersant was formed from 70% DADMAC and 30% dimethylaminoethylacrylate benzyl chloride quaternary (DMAEA.BCQ) monomers. The following reagents were used: 188.03 g 62% Solution of DADMAC 104.28 g 80% Solution of DMAEA.BCQ 0.20 g Versene 15.00 g 25% Solution of Ammonium Persulfate 692.49 g Deionized Water DADMAC and 100 g of deionized water were placed within a polymerization reaction vessel which was purged with nitrogen at 10 ml/min. Thereafter, the ammonium persulfate was added dropwise to the reaction vessel via a syringe pump for 2 hours. Simultaneously, DMAEA.BCQ was added dropwise to the reaction vessel via a syringe pump for 2 hours. The DMAEA.BCQ was diluted with 100 g of deionized water prior to being loaded into the syringe pump. Thereafter, the remaining deionized water and versene were added to the reaction vessel which was then heated at 65°C for 6 hours. Preparation - Example 3 A dispersant was formed from 70% DADMAC and 30% dimethylaminoethylacrylate benzyl chloride quaternary (DMAEA.BCQ) monomers. The following reagents were used: 188.03 g 62% Solution of DADMAC 104.28 g 80% Solution of DMAEA.BCQ 0.20 g Versene 1.17 g V50 706.00 g Deionized Water 0.32 g H 2 SO 4 DADMAC was placed within a polymerization reaction vessel which was purged with nitrogen at 10 ml/min., stirred at 300 rpm and a torque of 3,5 · 10 -5 N·m (350 dynes-cm). The pH was adjusted to 3.5 by addition of H 2 SO 4 . To this was added dropwise V50 and DMAEA.BCQ via separate syringe pumps. The DMAEA.BCQ was diluted with 100 g of deionized water. During the first 40 minutes of addition the torque gradually increased to 2,24·10 -4 N·m (240 dynes-cm). Thereafter, 100 g of deionized water was pded to the DADMAC which reduced the torque to 8,5·10 -5 N·m (850 dynes-cm). The reaction vessel was then heated at 65°C for 5 hours. After 2 hours and 20 minutes the torque reached 2,9·10 -4 N·m (2920 dynes-cm). 100 g of deionized water was again added which reduced the torque to 1,18·10 -4 N·m (1180 dynes-cm) After 3 hours and 15 minutes another 100 g of deionized water was added to the polymerizing product. After 5 hours another 100 g of deionized water was added to the reaction vessel and the temperature was raised to 80°C for 1 hour. Thereafter, the resulting polymer was diluted with the remaining deionized water, cooled and stored. Preparation - EXAMPLE 4 A dispersant was formed from 80% DADMAC and 20% dimethylaminoethylmethacrylate cetyl chloride quaternary (DMAEM.CCQ) monomers. The following reagents were used: 188.02 g 62% Solution of DADMAC 83.43 g DMAEM.CCQ 0.20 g Versene 1.17 g V50 727.03 g Deionized Water 0.15 g H 2 SO 4 DADMAC was placed within a polymerization reaction vessel which was purged with nitrogen at 10 ml/min. and stirred at 300 rpm. The pH was adjusted to 3.5 by addition of H 2 SO 4 . 150 ml of deionized water was added to the DADMAC. This was followed by the dropwise addition of V50 and DMAEA.CCQ via separate syringe pumps for 2 hours. The DMAEA.CCQ was diluted with 100 g of deionized water. The reaction vessel was then heated at 65°C for 4.5 hours. Between 1.5 to 2 hours 180 ml of deionized water was again added. After 4.5 hours the temperature was raised to 70°C for 0.5 hours. Thereafter, the resulting polymer was diluted with the remaining deionized water, cooled and stored. Preparation - EXAMPLE 5 A dispersant was formed using the same technique described in Example 4 above from 80% DADMAC and 20% dimethylaminoethylacrylate benzyl chloride quaternary (DMAEA.BCQ) monomers. The following reagents were used: 227.52 g 62% Solution of DADMAC 73.68 g 80% Solution of DMAEA.BCQ 0.40 g Versene 1.42 g V50 696.63 g Deionized Water 0.35 g H 2 SO 4 However, the water was added as needed. Table 1 below sets forth the time of deionized water addition during the semi-batch polymerization process. SPEED OF ROTATION(rpm) TORQUE in 10 -5 N·m (DYNES-CM) TIME H 2 O ADDITION 200 4,0 (400) 0 0 200 8,5 (850) 30 min. 0 200 12,0 (1200) 45 min. 50 g 200 7,0 (700) 46 min. - 200 16,0 (1600) 1 hr. 10 min. 50 g 200 10,0 (1000) 1 hr. 11 min. - 200 15,1 (1510) 1 hr. 35 min. 50 g 200 12,0 (1200) 1 hr. 36 min. 50 g 200 6,5 (650) 1 hr. 37 min. - 200 15,0 (1500) 1 hr. 55 min. - 200 16,1 (1610) 2 hr. 12 min. 50 g 200 5,58 (558) 2 hr. 13 min. - Preparation - EXAMPLE 6 A dispersant was formed from 90% DADMAC and 10% dimethylaminoethylacrylate benzyl chloride quaternary (DMAEA.BCQ) monomers. The following reagents were used: 251.79 g 67% Solution of DADMAC 39.13 g 80% Solution of DMAEA.BCQ 0.20 g Versene 3.36 g V50 678.00 g Deionized Water 27.52 g NaCl The semi-batch procedure was as follows: (1) A DADMAC solution was prepared by evaporating 272.10 g of of DADMAC monomer (62% actives) for 30 minutes. A solution comprising 251.79 g of a 67% solution of DADMAC and 27.52 g of NaCl was placed in a reactor. (2) The polymerization reaction vessel was then purged with nitrogen, stirred at 200 rpm and heated to 57°C. (3) Then 40 mg of versene were added to the reaction vessel. (4) 39.13 g of DMAEA.BCQ were diluted with 15.87 g of deionized water, then 160 mg of versene were added, stirred and loaded into a syringe pump. (5) 500 g of water were disposed in a funnel adjacent to the reaction vessel and nitrogen sparged continuously. (6) 1.68 g of V50 were dissolved in 45.16 g of deionized water and loaded into another syringe pump. (7) At 57°C, 11.7 g of the V50 solution were added to the reaction vessel, together with the dropwise addition of the DMAEA.BCQ. (8) Additional deionized water was added from time to time as required. (9) After 5 hours the temperature was raised to 82°C for 1 hour. (10) Thereafter, the resulting polymer was diluted with the remaining deionized water, cooled and stored. This example was also performed without any sodium chloride. The dispersant obtained was identical in all respects to the above dispersant which utilized sodium chloride during its formation. EXAMPLE 1 A dispersion of a water soluble cationic polymer was formed from the terpolymer of 65 mole % acrylamide (AcAm), 25 mole % dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ), and 10 mole % dimethylaminoethyl acrylate methyl chloride quaternary (DMAEA.MCQ). Initially, 40.336 g of water, 14.405 g of AcAm (48.2%), 12.678 g of DMAEA.BCQ (80%), 3.621 g of DMAEA.MCQ (80.5%), 4.930 g of a dispersant comprising a copolymer of 90 mole % DADMAC and 10 mole % DMAEA.BCQ, 16 g of ammonium sulfate, and 0.6 g of glycerin were added to a conventional latex reaction vessel. The reaction vessel was degassed for approximately 30 minutes with nitrogen at 9 ml/min. The reaction mixture was heated to approximately 50°C during the degassing and stirred at 400 rpm. After the 30 minutes of degassing at 9 ml/min., the nitrogen was reduced to 2 ml/min. and 0.4 g of a 1% solution of a V50 and 0.03 g of versene were added to the reaction vessel. Thereafter, the reaction vessel was heated for another 4 hours at 50°C to obtain the final water soluble polymer dispersion. The final product was filtered through a 100 mesh screen (aperture 0,15 mm) and <0.8 wt.% unfiltered material was removed. The torque at Time = 0 was 5,08·10 -5 N·m (508 dynes.cm) at 402 rpm. The maximum torque observed during the polymerization process was 8,2·10 -5 N·m (820 dynes.cm) at approximately 400 rpm. The final torque was 5,1·10 -5 N·m (510 dynes-cm). The resulting polymer dispersion exhibited a viscosity of 257.5 mPa·s (cp). EXAMPLE 2 A dispersion of a water soluble cationic polymer was formed from the copolymer of 90 mole % acrylamide (AcAm) and 10 mole % dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ). Initially, 40.987 g of water, 20.528 g of AcAm (48.4%), 8.387 g of DMAEA.BCQ (50%), 4.712 g of AcAm/DMAEA.BCQ (90/10 mole %), 2.12 g of a dispersant comprising a copolymer of 90 mole % DADMAC and 10 mole % DMAEA.BCQ, 15.55 g of ammonium sulfate, and 0.7 g of glycerin, and 0.566 g of acetic acid were added to a conventional latex reaction vessel. The reaction vessel was degassed for approximately 30 minutes with nitrogen at 9 ml/min. The reaction mixture was heated to approximately 40°C during the degassing and stirred at 400 rpm. After the 30 minutes of degassing at 9 ml/min., the nitrogen was reduced to 2 ml/min. and 0.566 g of a 1% solution of a VA044 and 0.03 g of versene were added to the reaction vessel. Thereafter, the reaction vessel was heated for another 4 hours at 40°C to obtain the final water soluble polymer dispersion. The reaction mixture was cooled to ambient temperature, and 6.22 g of sodium sulfate and 0.566 g of acetic acid were added. The viscosity at Time = 0 was 16 mPa·s (cp) at 400 rpm, at 25° C. The maximum viscosity observed during the polymerization process was 2100 mPa·s (cp) at 40°C. The final viscosity was 1000 mPa·s (cp). The polymer dispersion after post-treatment exhibited a viscosity of 37.5 mPa·s (cp). EXAMPLE 3 A dispersion of a water soluble cationic polymer was formed from the terpolymer of 70 mole % acrylamide (AcAm), 20 mole % dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ), and 10 mole % dimethylaminoethyl acrylate methyl chloride quaternary (DMAEA.MCQ). Initially, 31.918 g of water, 17.229 g of AcAm (46.8%), 17.5 g of DMAEA.BCQ (50%), 3.903 g of DMAEA.MCQ (80.5%), 4.931 g of a dispersant comprising a copolymer of 90 mole % DADMAC and 10 mole % DMAEA.BCQ, 16.089 g of ammonium sulfate, and 0.6 g of glycerin were added to a conventional latex reaction vessel. The reaction vessel was degassed for approximately 30 minutes with nitrogen at 9 ml/min. The reaction mixture was heated to approximately 48°C during the degassing and stirred at 400 rpm. After the 30 minutes of degassing at 9 ml/min., the nitrogen was reduced to 2 ml/min. and 0.4 g of a 1% solution of a V50 and 0.03 g of versene were added to the reaction vessel. Thereafter, the reaction vessel was heated for another 4 hours at 48°C to obtain the final water soluble polymer dispersion. 6 g of ammonium sulfate and 1 g of acetic acid were added to this polymer dispersion. The viscosity at Time = 0 was 12 mPa·s (cp) at 400 rpm. The maximum viscosity observed during the polymerization process was 1600 mPa·s (cp). The polymer dispersion after post-treatment exhibited a viscosity of 250 mPa·s (cp). EXAMPLE 4 A dispersion of a water soluble cationic polymer was formed from the terpolymer of 65 mole % acrylamide (AcAm), 25 mole % dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ), and 10 mole % dimethylaminoethyl acrylate methyl chloride quaternary (DMAEA.MCQ). Initially, 40.336 g of water, 14.405 g of AcAm (48.2%), 12.678 g of DMAEA.BCQ (80%), 3.621 g of DMAEA.MCQ (80.5%), 4.930 g of a dispersant comprising a copolymer of 90 mole % DADMAC and 10 mole % DMAEA.BCQ, 16 g of ammonium sulfate, 0.9 g of glycerin, and 1 g of acetic acid were added to a conventional latex reaction vessel. The reaction vessel was degassed for approximately 30 minutes with nitrogen at 9 ml/min. The reaction mixture was heated to approximately 48°C during the degassing and stirred at 400 rpm. After the 30 minutes of degassing at 9 ml/min., the nitrogen was reduced to 2 ml/min. and 0.4 g of a 1% solution of a V50 and 0.03 g of versene were added to the reaction vessel. Thereafter, the reaction vessel was heated for another 4 hours at 48°C to obtain the final water soluble polymer dispersion. Then 6 g of ammonium sulfate and 1 g of acetic acid were added to the polymer dispersion. The Brookfield viscosity at Time = 0 was 12 mPa·s (cp). The maximum viscosity observed during the polymerization process was 1700 mPa·s (cp) (#3 spindle, at 12 rpm). The polymer dispersion after post-treatment exhibited a Brookfield viscosity of 86 mPa·s (cp) (#1 spindle at 60 rpm). EXAMPLE 5 A dispersion of a water soluble cationic polymer was formed from the terpolymer of 65 mole % acrylamide (AcAm), 25 mole % dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ), and 10 mole % dimethylaminoethyl acrylate methyl chloride quaternary (DMAEA.MCQ). Initially, 40.336 g of water, 14.405 g of AcAm (48.2%), 12.678 g of DMAEA.BCQ (80%), 3.621 g of DMAEA.MCQ (80.5%), 4.930 g of a dispersant comprising a copolymer of 90 mole % DADMAC and 10 mole % DMAEA.BCQ, 15.50 g of ammonium sulfate and 1.2 g of glycerin were added to a conventional latex reaction vessel. The reaction vessel was degassed for approximately 30 minutes with nitrogen at 9 ml/min. The reaction mixture was heated to approximately 48 °C during the degassing and stirred at 1000 rpm. After the 30 minutes of degassing at 9 ml/min., the nitrogen was reduced to 2 ml/min. and 0.4 g of a 1% solution of a V50 and 0.03 g of versene were added to the reaction vessel. Thereafter, the reaction vessel was heated for another 4 hours at 48°C to obtain the final water soluble polymer dispersion. Then 6.5 g of ammonium sulfate and 1 gram of acetic acid were added to the polymer dispersion. The Brookfield viscosity at Time = 0 was 10 mPa·s (cp). The maximum viscosity observed during the polymerization process at approximately 1000 rpm was 3200 mPa·s (cp). The polymer dispersion after post-treatment exhibited a Brookfield viscosity of 82 mPa·s (cp)(#1 spindle at 60 rpm). EXAMPLE 6 A dispersion of a water soluble cationic polymer was formed from the terpolymer of 65 mole % acrylamide (AcAm), 25 mole % dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ), and 10 mole % dimethylaminoethyl acrylate methyl chloride quaternary (DMAEA.MCQ). Initially, 40.336 g of water, 14.405 g of AcAm (48.2%), 12.678 g of DMAEA.BCQ (80%), 3.621 g of DMAEA.MCQ (80.5%), 4.930 g of a dispersant comprising a copolymer of 90 mole % DADMAC and 10 mole % DMAEA.BCQ, 15.50 g of ammonium sulfate and 1.2 g of glycerin were added to a conventional latex reaction vessel. The reaction vessel was degassed for approximately 30 minutes with nitrogen at 9 ml/min. The reaction mixture was heated to approximately 48 °C during the degassing and stirred at 1000 rpm. After the 30 minutes of degassing at 9 ml/min., the nitrogen was reduced to 2 ml/min. and 0.13 g of a 1% solution of a V50 and 0.03 g of versene were added to the reaction vessel. Thereafter, the reaction vessel was heated for another 3 hours at 48°C and a second batch of V50 initiator (0.27 g) was added. The reaction proceeded for a further hours (total reaction time was 4 hours) to obtain the final water soluble polymer dispersion. Then 6.5 g of ammonium sulfate and 1 g of acetic acid were added to the polymer dispersion. The Brookfield viscosity at Time = 0 was 12 mPa·s (cp). The maximum viscosity observed during the polymerization process at approximately 1000 rpm was 1600 mPa·s (cp). The polymer dispersion after post-treatment exhibited a Brookfield viscosity of 70 mPa·s (cp) (#1 spindle at 60 rpm). EXAMPLE 7 The following is a comparative study of the use of conventional dispersant in the preparation of a water soluble polymer dispersion comprising 90 mole % acrylamide and 10 mole % DMAEA.BCQ in a three liter reactor. All of the samples set forth in Table 2 below yielded polymer dispersions without any significant gel formation. These dispersions also met the usual RSV/IV specifications; however, these samples proceeded through high process viscosities (i.e., 100,000 to >500,000 mPa·s (cp). Such high process viscosities require the use of custom built polymerization reaction vessels which are costly and inconvenient due to all of the conventional latex reaction vessel currently in use. The last entry in Table 2 exemplifies the efficiency of hydrophobic stabilizer in preparation of a polymer dispersion. [Dispersion of AcAm/DMAEA.BCQ] Sample No. Dispersant Peak Visc. (cps) mPa·s RSV/IV (dL/gm) 1 poly(DMAEA.MCQ) >500,000 19.6/15.98 2 AcAm-co-DMAEA.MCQ >300,000 19.2/15.36 3 DADMAC-co-DMAEA.BCQ 2100 19.9/16.20 EXAMPLE 8 The following experiments were conducted to determine whether the dispersant used according to the present invention would reduce the process viscosity of the polymerization of a dispersion comprising a terpolymer of 65 mole % acrylamide, 25 mole % DMAEA.BCQ and 10 mole % DMAEA.MCQ. A 1000 g batch of the aforementioned terpolymer was prepared using either a poly(DMAEA.MCQ) dispersant or a dispersant comprising 90 mole % of DADMAC and 10 mole % of DMAEA.BCQ. The results are set forth below in Table 3. [AcAm/DMAEA.BCQ/DMAEA.MCQ Dispersant] Run No. Dispersant Peak Viscosity 1 poly(DMAEA.MCQ) >100,000 mPa·s (cp) 2 DADMAC/DMAEA.BCQ 1,700 mPa·s (cp) Samples were withdrawn every 15 minutes and the Brookfield viscosity measured. The peak viscosity measured during run no. 1 using the conventional dispersant was >100,000 mPa·s (cp); whereas run no. 2 using the hydrophobic dispersant of the present invention exhibited a peak viscosity of only 1,700 mPa·s (cp). This comparison clearly indicates that the dispersant is capable of substantially reducing the process viscosity during polymerization of water soluble polymer dispersions. EXAMPLE 9 The effect of hydrophobic stabilizers in reducing the process viscosities during the dispersion polymerizations was further investigated and the results are set forth below in Table 4. Run# Polymer Stabilizer Peak viscosities mPa·s (cp) RSV/IV dL/gm 1 AcAm/DMAEA.BCQ(90/10) DADMAC/DMAEA.BCQ 90 18.9/15.8 2 AcAm/DMAEA.BCQ/DMAEA.MCQ DADMAC/DMAEA.BCQ 2100 21.6/16/2 3 AcAm/DMAEA.BCQ/DMAEA.MCQ DADMAC/DMAEA.BCQ 1600 19.6/15.2 4 AcAm/DMAEA.BCQ/DMAEA.MCQ DADMAC/DMAEA.BCQ 50,000 Gelled 5 AcAm/DMAEA.BCQ/DMAEA.MCQ DADMAC/DMAEA.BCQ 700 21.6/15.8 6 AcAm/DMAEA.BCQ/DMAEA.MCQ DADMAC/DMAEA.BCQ 2100 20.8/15.8 7 AcAm/DMAEA.BCQ(90/10) DADMAC/DMAEA.BCQ 600 19.9/16.2 8 AcAm/DMAEA.BCQ/DMAEA.MCQ DADMAC/DMAEA.BCQ 3000 20.1/15.2 9 AcAm/DMAEA.BCQ/DMAEA.MCQ DADMAC/DMAEA.BCQ 1800 19.6/15.3 10 AcAm/DMAEA.BCQ(90/10) DADMAC/EHA 720 20.8/15.6 The initiator used in the preparation of the dispersants was found to influence their efficiency in the dispersion process. Initiators like V50 and VA044 appeared to function very efficiently in reducing the process viscosities of dispersion polymerizations; whereas initiators like ammonium persulfate appeared to cause very high viscosities and resulted in the formation of a polymer gel as shown in run no. 4. Table 4 above also demonstrates the efficiency of a DADMAC/EHA dispersant in reducing the process viscosity during polymerization of a water soluble polymer.

Claims: A process for preparing a water-soluble polymer dispersion which comprises polymerizing a water-soluble mixture comprising (a) a cationic monomer represented by general formula (I): where R 1 is either hydrogen or CH 3 ; R 2 and R 3 are each an alkyl group having 1 to 3 carbon atoms; A 1 is either an oxygen atom or NH; B 1 is either an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group, and X 1 ⊖ is an anionic counterion, and optionally (b) a second cationic monomer represented by general formula (II): where R 4 is either hydrogen or CH 3 ; R 5 and R 6 are each an alkyl group having 1 to 2 carbon atoms; R 7 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms; A 2 is either an oxygen atom or NH; B 2 is either an alkylene group having 2 to 4 carbon atoms or a hydroxypropylene group, and X 2 ⊖ is an anionic counterion, and (c) (meth)acrylamide in an aqueous solution of a polyvalent anion salt, the process comprises: conducting said polymerization in the presence of a polymerization initiator and a hydrophobically associating dispersant comprising a copolymer of diallyldimethylammonium chloride and a hydrophobic monomer selected from the group consisting of C 6 -C 20 N-substituted quaternary dialkylaminoalkylacrylates (DMAEA), C 6 -C 20 N-substituted quaternary dialkylaminoalkylmethacrylates (DMAEM), C 6 -C 20 N-substituted quaternary dialkylamino-alkyl(meth)acrylamides, and alkyl esters of acrylic acid, in a molar ratio of diallyldimethylammonium chloride to hydrophobic monomer in the range between 99:1 and 20:80, wherein said cationic monomer represented by formula (I) (monomer (a) being present in an amount between 5 and 50 mole%, said cationic monomer represented by formula (II) (monomer (b)) optionally being present in an amount between 5 and 50 mole%, said (meth)acrylamide (monomer (c)) being present in an amount in the range between 20 and 95 mole%, and said hydrophobically associating dispersant being present in an amount between 2.5 and 10 weight%, based on the total weight of monomers (a), (b) and (c). The process of claim 1 wherein the dispersant is a copolymer of diallyldimethylammonium chloride and a monomer selected from the group consisting of dimethylaminoethylacrylate benzyl chloride quaternary and dimethylaminoethylacrylate cetyl chloride quaternary. The process of claim 1 wherein the dispersant is a copolymer of diallyldimethylammonium chloride and a monomer selected from the group consisting of dimethylaminoethylmethacrylate benzyl chloride quaternary and dimethylaminoethylmethacrylate cetyl chloride quaternary. The process of any of claims 1 to 3 wherein said alkyl ester of acrylic acid is ethyl hexyl acrylate. The process of any of claims 1 to 4 wherein the monomers represented by formula (I) are selected from the group consisting of the benzylchloride quaternaries of dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide and dimethylhydroxypropyl (meth)acrylate, diethylaminopropyl (meth)acrylamide and dimethylaminohydroxypropyl (meth)acrylate. The process of any of claims 1 to 5 wherein the monomers represented by formula (II) are selected from the group consisting of the methyl and ethyl quaternary salts of dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide and dimethylhydroxypropyl (meth)acrylate. The process of any of claims 1 to 6 wherein the process viscosity during polymerization is less than about 5,000 mPa.s (cps). The process of any of claims 1 to 7 for preparing dispersions of cationic vinyl addition polymers in an aqueous salt solution.

Inventors: CRAMM JEFFREY R, RAMESH MARIAN, CRAMM, JEFFREY R., RAMESH, MARIAN
Applicants: NALCO CHEMICAL CO, NALCO CHEMICAL COMPANY
Application year: 1994
Main classification: C08F226
IPC codes: C08F26, C08F220, C08F226, C08F20, C08F2